Reiner Braun

Age: 17,
21 (after time skip)
Birthday: August 1
Height: 185 cm (6'1") -> 188 cm (6'2")
Weight: 95 kg (210 lbs) -> 83 kg (182 lbs)
Affiliations: 104th Trainees Squad, Scouting Legion
Graduation Rank: 2nd

Reiner Braun is strong willed, with a solid constitution. He is most adept at gaining the trust of his comrades. He is ranked no 2 of the trainee class and helps Eren out during his training days.

Major spoiler:

It is later revealed that Reiner is a Titan-Shifter. He is the Armored Titan that opened the gates of Wall Maria along with his partner Bertolt, the Colossal Titan, with the intention of slaughtering the wall's inhabitants.
Note: Reiner Braun is the official English translation by Kodansha.